Element having bimetal properties

ABSTRACT

The subject of this invention is an element having bimetal properties and made of a composite fiber material comprising a matrix material and at least one group of fibers embedded therein. The bimetal properties may be achieved by using a matrix material having a coefficient of thermal expansion differing from that of at least one group of embedded fibers. Alternatively, the coefficients of thermal expansion of at least two groups of embedded fibers may differ from each other to achieve such properties. Yet another possibility is to combine these two methods to achieve the desired bimetal properties.

United States Patent Schneider et al.

ELEMENT HAVING BIMETAL PROPERTIES Inventors: Friedrich Schneider; DieterStockel,

both of Pforzheim, Germany Assignee: G. Rau, Pforzheim, Germany Filed:June 26, 1972 Appl. No.: 266,351

Foreign Application Priority Data July 20, 1971 Germany 2136171 US. Cl.73/3635 Int. Cl. G01k 5/62 Field of Search 73/3635, 363, 363.1;

References Cited UNITED STATES PATENTS 12/1927 Steel 29/195.5

3,107,532 10/1963 Lingnau ..73/363.5

Primary Examiner-Donald O. Woodiel Attorney, Agent, or FirmWenderoth,Lind & Ponack [5 7] ABSTRACT The subject of this invention is an elementhaving bimetal properties and made of a composite fiber materialcomprising a matrix material and at least one group of fibers embeddedtherein. The bimetal properties may be achieved by using a matrixmaterial having a coefficient of thermal expansion differing from thatof at least one group of embedded fibers. Alternatively, thecoefficients of thermal expansion of at least two groups of embeddedfibers may differ from each other to achieve such properties. Yetanother possibility is to combine these two methods to achieve thedesired bimetal properties.

10 Claims, 3 Drawing Figures PATENTEDHAR 12 I974 3. 796. 1 0Ooooooooooodooq O06 O00 5 7.2 j

o 0 0 o 0L0 o o 0 0p 0 ELEMENT HAVING BIMETAL PROPERTIES BACKGROUND OFTHE INVENTION The invention relates to an element having bimetalproperties which can be used in palce of the known bimetal elements fortemperature-dependent regulation or control functions or for theindication of temperature.

Bimetal elements are known in a very wide variety of forms for use inindicating temperature and in initiating control operations independence upon temperature. These bimetal elements consist of at leasttwo different inseparably connected layers of metal or non-metallicmaterial having different coefficients of thermal expansion. Since, whenheated, one of the layers expands to a greater extent than the other,bimetallic elements of this kind bend on a change of temperature, theextent of bending being dependent upon the difference in thecoefficients of thermal expansion of the material of the individuallayers.

Bimetallic elements can be used in either of two ways: their freeunrestricted deflection, dependent upon temperature, may be used such asin bimetal spiral thermometers, or thermal power may be produced bylargely completely suppressing the deflection of the element such powerdoing mechanical work and displacing regulating elements (e.g. bimetalignition means in gas-heated equipment).

The known forms of bimetallic elements mainly consist of materialshaving different coefficients of thermal expansion secured together bywelding, soldering, bonding and the like.

The known bimetallic elements do not fulfil all the important practicalrequirements. A particular disadvantage resides in the fact that withrelatively broad bimetal strips the isotropy of the thermal expansionresults in a very undesirable transverse curvature in addition to therequired longitudinal bending, and this transverse curvature leads tomechanical stiffening of the strip. In this way, the required deflectionis partly inhibited. In the known forms of bimetallic elements, whichare based mainly on combinations of iron-nickel alloys, the choice ofmaterial is primarily determined by the thermal properties of theconnected layers. This of necessity means that disadvantageousproperties as regards electrical conductivity, corrosion-resistanceetc., have to be accepted.

SUMMARY OF THE INVENTION An object of the present invention is toeliminate the above-stated disadvantages and to provide a bimetalelement which possesses particularly advantageous properties. Theinvention is mainly characterized in that the element is made of acomposite fiber material comprising at least one metallic component.Composite fiber materials of this kind contain randomly or specificallydistributed fibers embedded in a matrix material, and in a preferredform, both the matrix material and the fibers are made of metallicmaterials. The composite fiber material can be produced by knownmetallurigcal methods, based for example on powder metallurgy, but it isadvantageously produced by jointly coldshaping the matrix and fibermaterials. The term composite fiber material is not, however, intendedto be limited exclusively to purely metallic combinations in the presentcase, since for specific uses composite fiber materials of which thematrix or fiber material is nonmetallic, e.g. plastics material, can beproduced.

To achieve the bimetal properties in an element in which the compositefiber material comprises a first component constituted by a matrixmaterial and a second component constituted by at least one group offibers embedded in the matrix material, it is advantageous that there isa coefficient of thermal expansion difference between the first andsecond components and/or between groups of fibers of the secondcomponent. Thus it is advantageous if the coefficients of thermalexpansion of at least two groups of fibers embedded in the matrixmaterial of the composite fiber material differ from each other, or if amatrix material is selected that has a coefficient of thermal expansiondiffering from that of at least one group of fibers embedded in thematrix material. These two possible methods may be combined with eachother.

Where the bimetallic effect results from the differing coefficients ofthermal expansion of embedded groups of fibers, the matrix material canbe freely selected to meet particular additional requirements, namely,corrosion-resistance, specific weight, electrical and thermalconductivity, good mechanical deformability etc. Similarly, the fiberscan be selected not only with the required coefficients of thermalexpansion in mind, but also with a view to obtaining the necessarymechanical properties, electrical resistance, magnetic properties and soon. Use may also be made of combinations of materials as normallyemployed in the known bimetal elements. A considerable advantage of theelement of the invention resides in the fact that the matrix materialmay be selected largely independently of the choice of the fiber thatresult in deflection of the element under the effect of heat.Furthermore, elements made of a composite fiber material do not becomerigid, due to the isotropy of the thermal expansion, as do the knownelements in the form of strips. The elements of the invention providelarge deflections and large return forces.

In accordance with a further advantageous feature of the invention, theentire cross-sectional area of a group of fibers having a lowcoefficient of thermal expansion may be greater than the entirecross-sectional area of a group of fibers having a higher coefficient ofthermal expansion, since generally the selected matrix materialreinforces the expansion of the group of fibers having the highercoefficient.

Groups of fibers can be distributed in the matrix ma terial in variousways and in accordance with the required defiectional movement. In oneadvantageous form, the groups of fibers can be arranged in parallellayers; this arrangement appears to be particularly suitable in the caseof elements in the form of strips. On the other hand, the use of thecomposite fiber material offers the possibility of making a torsionalbimetal element in the form of a strip, this being achieved by arranginga group or groups of fibers over the crosssection of the matrix materialin such a way that a temperature-responsive torsional moment results. Inthis connection, an asymmetric distribution of the groups of fibers inan element in the form of a strip is expedient, so that correspondingtorsional moments can be obtained.

A further important improvement may be achieved by embedding, in theelement, insulated fibers for electrical heating purposes and/or forconducting current.

By incorporating heating fibers or by appropriately selecting the fibersforming the fiber material, e.g., using the known nickel-iron alloys,which exhibit advantageous coefficients of thermal expansion as well asgood electrical resistance properties, a thermoelectric, directlyheatable control element can be formed in a simple manner.

The elements may be produced with a wide variety of cross-sectionalforms having cornered and circular contours. Also, the dimensions of theelements can be suited to meet particular requirements.

BRIEF DESCRIPTION OF THE DRAWINGS Examples of elements having bimetalproperties in accordance with the invention are illustrated in theaccompanying drawings in which:

FIG. 1 is a perspective view of a sectioned element in which groups offibers are distributed in parallel layers;

FIG. 2 shows an element having torsional properties, and

FIG. 3 shows an element in which there are groups of fibers havingdifferent cross-sectional dimensions.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows an element in theform of a strip and made of metallic matrix material 1 in which areembedded a first group 3 of metallic fibers having a low coefficient ofthermal expansion and a second group 2 of metallic fibers having ahigher coefficient of thermal expansion. When the element is heated, thestrip acquires a convex upward curvature.

In the example illustrated in FIG. 2, the group of f1- bers 3 having thelower coefficient of thermal expansion is asymmetrically arranged inrelation to the group 2 having the higher coefficient of thermalexpansion so as to produce a torsional moment. When the element isappropriately heated, the strip 1 of matrix material twists about itslongitudinal axis, so that direct rotary movements can be initiated in aparticularly advantageous manner.

In the form shown in FIG. 3, the matrix material 1 is so selected thatit reinforces the expansion of the second group 2 of fibers having thehigher coefficient of thermal expansion, and it will be seen that thecrosssectional distribution of the fibers of group 3 differs from thatof the fibers of group 2. Also in this form insulated resistance-heatingwires 4 are embedded between the two groups of fibers so that thestrip-like element can be directly heated.

We claim:

1. A composite element having bimetallic properties and comprising:

a first component comprising a matrix material and having imbeddedtherein at least one additional component, each of said at least oneadditional components comprising a group of fibers;

at least one of said components being metal; and

one of said components having a coefficient of thermal expansiondifferent from that of at least another of said components.

2. An element as claimed in claim 1, wherein said at least oneadditional component comprises a single group of fibers, and whereinsaid matrix material has a coefficient of thermal expansion differentfrom that of said single group of fibers.

3. An element as claimed in claim I, wherein said at least oneadditional component comprises second and third additional components,each of said second and third components comprising a group of fibers.

4. An element as claimed in claim 3, wherein said matrix material has acoefficient of thermal expansion different from that of one of saidgroups of fibers.

5. An element as claimed in claim 3, wherein the group of fibers of saidsecond component has a coefficient of thermal expansion different fromthat of the group of fibers of said third component.

6. An element as claimed in claim 5, wherein the total cross-sectionalarea of the fibers of that group having the lower coefficient of thermalexpansion is greater than the total cross-sectional area of the fibersof that group having the higher coefficient of thermal expansion.

7. An element as claimed in claim 5, wherein said groups of fibers ofsaid second and third components are arranged in separate layers in saidmatrix material, said layers being parallel.

8. An element as claimed in claim 5, wherein said group of fibers ofsaid second component are imbedded in said matrix materialasymmetrically of said group of fibers of said third component, wherebya temperature responsive torsional moment is created in said element.

9. An element as claimed in claim 1, further comprising electricallyconductive fibers imbedded in said matrix material.

10. An element as claimed in claim 9, wherein said electricallyconductive fibers form resistance heating

1. A composite element having bimetallic properties and comprising: afirst component comprising a matrix material and having imbedded thereinat least one additional component, each of said at least one additionalcomponents comprising a group of fibers; at least one of said componentsbeing metal; and one of said components having a coefficient of thermalexpansion different from that of at least another of said components. 2.An element as claimed in claim 1, wherein said at least one additionalcomponent comprises a single group of fibers, and wherein said matrixmaterial has a coefficient of thermal expansion different from that ofsaid single group of fibers.
 3. An element as claimed in claim 1,wherein said at least one additional component comprises second andthird additional components, each of said second and third componentscomprising a group of fibers.
 4. An element as claimed in claim 3,wherein said matrix material has a coefficient of thermal expansiondifferent from that of one of said groups of fibers.
 5. An element asclaimed in claim 3, wherein the group of fibers of said second componenthas a coefficient of thermal expansion different from that of the groupof fibers of said third component.
 6. An element as claimed in claim 5,wherein the total cross-sectional area of the fibers of that grouphaving the lower coefficient of thermal expansion is greater than thetotal cross-sectional area of the fibers of that group having the highercoefficient of thermal expansion.
 7. An element as claimed in claim 5,wherein said groups of fibers of said second and third components arearranged in separate layers in said matrix material, said layers beingparallel.
 8. An element as claimed in claim 5, wherein said group offibers of said second component are imbedded in said matrix materialasymmetrically of said group of fIbers of said third component, wherebya temperature responsive torsional moment is created in said element. 9.An element as claimed in claim 1, further comprising electricallyconductive fibers imbedded in said matrix material.
 10. An element asclaimed in claim 9, wherein said electrically conductive fibers formresistance heating elements.